Equity Incentive Plans - Number and Weighted Average Grant-Date Fair Value of Unvested Stock Options (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Beginning Balance, Number of Options	3,077,481	2,008,960	1,957,760
Granted options during the period, Number	455,000	1,319,500	181,125
Forfeited options during the period, Number	(8,360)	(95,271)	(39,920)
Exercised options during the period, Number	(579,476)	(155,708)	(90,005)
Outstanding Ending Balance, Number of Options	2,944,645	3,077,481	2,008,960
Unvested options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding Beginning Balance, Number of Options	1,350,590	796,514	1,327,825
Granted options during the period, Number	455,000	1,319,500	181,125
Vested options during the period, Number	(651,530)	(654,022)	(637,940)
Forfeited options during the period, Number	(7,106)	(74,335)	(37,215)
Exercised options during the period, Number	(148,784)	(37,067)	(37,281)
Outstanding Ending Balance, Number of Options	998,170	1,350,590	796,514
Unvested options at the beginning of the period, Weighted Average Grant-Date Fair Value	2.79	2.60	2.37
Granted options during the period, Weighted Average Grant-Date Fair Value	4.30	2.70	4.12
Vested options during the period, Weighted Average Grant-Date Fair Value	2.68	2.32	2.51
Forfeited options during the period, Weighted Average Grant-Date Fair Value	3.92	4.02	2.99
Exercised options during the period, Weighted Average Grant-Date Fair Value	2.46	1.87	2.11
Unvested options at the end of the period, Weighted Average Grant-Date Fair Value	3.69	2.79	2.60